We band the country into some broad areas starting in the north and working south.
Broadly speaking, the north of the country is high and dry and can be visited at any time of year.
Santiago has a Mediterranean climate so has pleasant enough weather year round though high summer (December through February) is very hot.
From June to September there is snow on the mountains and the ski resorts are open.
The Winelands to the south of the capital have a fairly benign climate year round.
From the Lake District to the far south winter is much more noticeable and you probably will not want to visit during the winter months (June – September).
The exception to this is the area around Torres del Paine which can be dry and calm in mid-winter.
Warm days, cold nights. In mid-winter (July-August) temperature ranges from 3-19°c with negligible rainfall. In summer (Dec-Mar) temperature ranges from 9-28°c with some chance of showers.
These temperatures relate to San Pedro which is in a fairly protected spot at 2,000m. On excursions, you can find yourself at altitudes of over 5,000m where temperatures can easily be -5°c with windchill on top.
Take 4 layers of clothing for the body, 2 for legs plus hat and gloves. The sun is fierce at this altitude.
Has a Mediterranean climate so even in the depths of winter (July-August) temperatures range from 5-15°c with rainfall of around 100mm. Even in winter, daytime temperatures tend to be pleasant in the city with a light jacket only really necessary at night.
In summer (December-March) temperatures rise dramatically to 20-35°c with negligible rainfall. The city tends to be very warm and muggy, light & loose clothing is ideal.
The main resorts of Portillo, Valle Nevado, and Chillan claim 80% sunny days in a season which runs from mid-June to the end of September.
When the sun is out, daytime temperatures can be quite pleasant with skiing in short sleeves not impossible.
Nights are obviously very cold as you are at around 2,500m-3,000m.
Lake District Weather
Expect high levels of precipitation at any time of year, particularly in the southern Lakes around Puerto Montt/Puerto Varas and Chiloe.
Pucon is inland and therefore has a relatively sunny and dry summer climate.
Conditions are usually such that you can comfortably spend daytime in shorts & t-shirt with a fleece only needed at night. A waterproof is always handy.
In winter (June-August) temperatures range from 4-12°c with quite a lot of rainfall.
Torres del Paine, i.e southern Patagonia, is on the same latitude, relatively speaking, as Manchester. You will also generally be at or near sea level.
Weather is therefore not extreme in and of itself.
Summer daytime temperatures can reach the 20°c dropping to around 10°c at night.
You can expect rain, wind and even snow at any time of year given the proximity of the ice fields.
In winter temperatures are generally 5-10°c during the day, falling back at night to around 0°c.
Levels of rainfall do not vary greatly by season though summer has slightly higher precipitation.
Winter is the time of year with least wind so can actually be a very nice time to visit, though days are shorter.